THE Yankees’ next All-Star hides behind a mask for three hours a day, but not when he goes out in public. He doesn’t need it then. His best friend on the team is the one who at times must wish he could conceal his identity with a mask.

They flock to Derek Jeter and politely nod at Jorge Posada. That’s the way it’s been for years. Little do they know Posada’s autograph some day soon will be worth a mint.

It will be on the same baseball as that of Pudge and Alex Rodriguez, Derek Jeter and Nomar Garciaparra, Cal Ripken Jr. and Rafael Palmeiro, an American League All-Star baseball.

If it doesn’t happen this season, it will happen soon enough. One year after a bewildering first-half littered with passed balls and strikeouts, Posada is headed in that direction.

Pudge will be voted the starter, and at this rate, Posada could be considered as a reserve, along with Boston’s Jason Varitek, Baltimore’s Charles Johnson and a few others who could get hot enough to merit a look.

Catchers take the longest to bloom because so much is involved in their jobs. That’s why so many catchers don’t reach their primes until they are with their second or third organization.

Switch-hitters can take a while to get it together, too, because they must work on their swing from both sides.

Posada, 28, was considered a question mark heading into this season because he never had handled every-day catching duties at the big-league level. Batting left-handed yesterday, Posada doubled off the wall in left-center to drive in the first run of the Yankees’ 3-1 win over the Orioles before a sellout crowd of 54,350 at the Stadium. It takes a lot of strength to hit a ball that far the other way. And it takes discipline to go with the pitch. The strength has been there for a while. The discipline is arriving.

Not even 16 hours earlier, batting right-handed, Posada pulled a three-run, ninth-inning home run to give the Yankees a 12-10 win over the Orioles.

Yesterday wasn’t a perfect day for Posada. He struck out with men on second and third and less than two outs, and he was charged with a passed ball. The good news: It was his first passed ball of the year and he has started behind the plate in 25 of the Yankees’ 28 games. By this time a year ago, when he was sharing the job with Joe Girardi, Posada already had six passed balls and a pair of multiple passed-ball games.

“It’s a lot tougher when you’re not playing every day,” Posada said of his defensive improvement.

So is hitting.

“He’s on a good run and he’s got a lot of confidence now,” Joe Torre said. “As long as he doesn’t try to do too much, he’ll be fine. He’ll be reminded constantly not to try to do too much.”

Posada is heeding that advice so far. He was asked what it would mean to him if he were selected to the All-Star team. If the question were a baserunner trying to steal second, he would have thrown it out by 15 feet. As it was, he threw it out before it was finished being asked.

“We’ve got a lot to go before thinking about that,” Posada said. “I’m just getting ready for tomorrow’s game. I’m not even looking past that.”

The hype arrives early here and it can affect an emerging ballplayer in one of three ways: a) make him conceited; b) turn him bitter about the new demands on his time; c) leave him unchanged.

A good-natured guy on the humble side, Posada isn’t likely to let the impending attention either eat him up or jack his ego.

He hasn’t hit his peak yet and he knows it. That keeps him pushing himself. To hear him tell it, it even turned him into a pest during spring training. He was determined to become a better hitter from the left side, and picking brains was part of the process to get there.

“I worked every day on staying level through the zone,” Posada said. “Short and level. I worked with Chris [Chambliss], [Don] Mattingly, Reggie Jackson. I was following people all over the place, asking so many questions I think they were getting tired of me.”

Posada batted .225 left-handed in 1999. This season, he’s batting .309 left-handed, .337 overall. All the attention given to his left-handed stroke hasn’t robbed his swing from the other side.

“We have to spend a lot of time in the batting cage,” Posada said of switch-hitters.

The day will come when Posada shares the batting cage with the best players in the world. It could even come this July in Atlanta.

But we’re getting way ahead of ourselves, something Torre will make sure Jorge doesn’t do.